Mirabegron is chemically described as (R)-2-(2-aminothiazol-4-yl)-N-(4-(2-((2-hydroxy-2-phenylethyl) amino) ethyl) phenyl) acetamide or (R)-2-(2-aminothiazol-4-yl)-4′-[2-[(2-hydroxy-2-phenylethyl) amino] ethyl]-acetanilide. It has the chemical formula (1) and is represented by the CAS registration no. 223673-61-8.

Mirabegron is an orally active beta-3-adrenoreceptor agonist approved by USFDA for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and urinary frequency.
U.S. Pat. No. 6,346,532 B1 (US'532) discloses Mirabegron or a salt thereof and process for its preparation. This patent, however, is silent about the crystal forms of Mirabegron. U.S. Pat. No. 7,342,117 (US'117) patent discloses two crystalline polymorphic forms of Mirabegron, the crystalline α-form and β-form. Said patent discloses the process for preparation of α-form crystal and β-form crystal of Mirabegron.
WO2012/156998A2 discloses processes for the preparation of α-form and β-form crystal of Mirabegron and pharmaceutical composition comprising thereof.
2588/MUM/2012 application discloses a crystalline form of Mirabegron and process for its preparation.
1562/MUM/2014 application discloses process for the preparation of α-form crystal of Mirabegron.
The method for the preparation of α-form crystal and β-form crystal of Mirabegron as per US'117 involves the use of water and ethanol as the only solvent. The process requires gradual or rapid cooling and use of seed material.
The methods for the preparation of crystalline α-form of Mirabegron described in the literature suffer from one or more drawbacks such as reproducibility, use of seed material, less yield and color development during preparation and upon storage which does not lead to an industrially sound process.
Therefore, there exists a need to develop consistent, cost effective and industrially feasible improved processes comprising means of preventing discoloration for the preparation of the hereinabove mentioned polymorphic form of Mirabegron.